Apparatus for supporting masonry walls against wind damage during construction

ABSTRACT

Bracing system for supporting masonry walls during construction utilizes metal braces arranged in opposed relation on opposite sides of the wall at spaced locations. Vertical support members are placed against each side of the wall and held tightly together by snap-tie members which are placed in the wall near its bottom during construction. Horizontal members extend outwardly from each vertical member and rest on the ground or on boards laid on the ground but are not anchored to the ground. Adjustable diagonal members connect the horizontal and vertical members to form a triangular brace on each side of the wall. The diagonal members are adjusted until the vertical members are pressed tightly against the wall adjacent their upper connections to the diagonal members. The weight of the braces are carried by the foundation, preferably by removable angle members laid over the edge of the foundation during construction. The angles include studs to which the horizontal members are attached. When building high walls, the wall is preferably supported as it reaches a height of about 10 or 12 feet. When the wall reaches a height of 20-24 feet, additional vertical members are linked to the previously positioned vertical members and pressed against the wall by additional diagonal members attached to the same horizontal members. The system permits the wall to resist moments as if it were supported as its top and bottom rather than as a cantilever and causes wind loads to be transferred through the masonry wall, into the brace, into the foundation wall and then into the ground. The system is quickly assembled and, except for the snap ties which are broken off inside the wall and covered over, reusable indefinitely.

United States Patent [191 Williams [4 June 18, 1974 [75] Inventor: relation on opposite sides of the wall at spaced locations. Vertical support members are placed against Asslgneei Bracmg Systems, -5 Wheaton, each side of the wall and held tightly together by snap- [22] Filed: Oct. 27, 1972 tie members which are placed in the wall near bottom during construction. Horizontal members extend PP ,665 outwardly from each vertical member and rest on the ground or on boards laid on the ground but are not 52 US. Cl 52/122, 52/149, 52/747, anchored Adjustable diagonal members 52/749 248 /3 5 4 R connect the horizontal and vertical members to form a 511 int. Cl. EtMg 21/02 triangular brace 9 each We of the The diagonal 58 Field of Search 52/745, 747, 749, 122, members are adlusted until the vettical members are 52/127 146, 149 168, 314; 243/354 5, 354 pressed tightly against the wall ad acent their upper R, 354 P, 354 C connections to the diagonal members. The weight of i the braces are carried by the foundation, preferably by [56] References Cited gemodvable zg gle members laid ovlelil' the eldge ofl tge oun ation urmg construction. e ang es lIlCU e UNITED STATES PATENTS studs to which the horizontal members are attached. $063,748 12/1936 When building high walls, the wall is preferably supported as it reaches a height of about 10 or 12 feet. 2832559 4/1958 When the wall reaches a height of 20-24 feet, addi- 239451662 7/1960 tional vertical members are linked to the previously 3,154833 11/1964 positioned vertical members and pressed against the 3,242,549 3/1966 wall by additional diagonal members attached to the 3,728,838 4/ 1973 same horizontal members. The system permits the wall 3.7 5.5 3 0/1973 to resist moments as if it were supported as its top and FOREIGN PATENTS OR APPLICATIONS bottom rather than as 8 Cfll'ltlifiV Bl' and causes wind 579 964 3/1955 Italy 52/149 loads to be transferred through the masonry wall, mto

Primary Examiner-Henry C. Sutherland Assistant Examiner-Carl D. Friedman Attorney, Agent, or Firm-Barry L. Clark APPARATUS FOR SUPPORTING MASONRY WALLS AGAINST WIND DAMAGE DURING CONSTRUCTION John G. Williams, Glen Ellyn, Ill.

[ 5 7] ABSTRACT Bracing system for supporting masonry walls during construction utilizes metal braces arranged in opposed the brace, into the foundation wall and then into the ground. The system is quickly assembled and, except for the snap ties which are broken off inside the wall and covered over, reusable indefinitely.

13 Claims, 8 Drawing Figures APPARATUS FOR SUPPORTING MASONRY WALLS AGAINST WIND DAMAGE DURING CONSTRUCTION BACKGROUND OF THE INVENTION During construction, masonry walls are very vulnerable to failure due to wind forces. Most walls are designed to span from the base, usually a foundation wall, to a support at the top, either a floor or roof. The design moment used for this type wall is W L/8 (where W is the load and L is the length between supports.) During construction, the wall only has a support at the base and the moment to be resisted is W L/2. It is obvious that the wall during construction must resist four times more moment than the wall is designed for. To resist these moments during erection, common practice is to prop wooden members, a 2 X 8 or 2 X 12, against the wall and fasten the other end to a stake driven into the ground. The horizontal spacing of these members varies greatly with individual contractors. In many instances, the stakes are driven very loosely into the ground by laborers who do not take the trouble to drive the stakes firmly or want to assure their easy removal. Extensive rain can also loosen the prop anchors. The wooden props, assembled in their usual manner, can resist very little wind loading and are mainly used to satisfy insurance requirements that bracing be used.

Obviously, when a wall blows over during construction there is a tremendous loss involved with respect to time and materials. Time must be spent in clearing away the debris. Also, if an additional supply of the building facing material is not readily available, the finishin g of the construction, and the work of other trades, is delayed, and increased in cost, to an extent much greater than the value of the time and materials required to rebuild the wall. Although most walls are insured against wind damage, the cost of the insurance must of course be high enough to cover the risk involved. Naturally,'the cost of insurance must be included in the cost of construction and causes building costs to be higher than they would be if the risk of falling walls was lower. Although insurance companies are concerned about walls blowing over during construction and usually require that bracing be used, the only bracing system currently being used is the wooden prop system previously described.

There are many prior art patents disclosing support devices for holding forms in place during construction and aligning door and window frames or other members. None of these patents, including U.S. Pat. Nos. Re 21,905, 1,779,007, 2,510,717, 2,514,397, 2,814,459, 3,006,592, 3,154,833, 3,444,659, 3,468,094 and 3,574,981 is concerned with supporting a modular wall against wind damage during construction. Most of the patents require that the horizontal or vertical support be anchored to the ground or a floor at its outer end and thus have the same problem as the conventional wooden prop system. Since walls go up so fast it is impossible for insurance investigators to check all bracing being used. Furthermore, after a wall has fallen it is impossible to determine how it was supported. Thus, it would be most desirable to have a wall support system which not only provides excellent support but which performs its function somewhat independently of the degree of care exercised by the workers installing the supports.

SUMMARY It is an object of this invention to provide a masonry support system which will permit a wall being constructed to resist wind loads of a magnitude equal to the design load of the finished wall (usually 15 pounds per square foot).

It is an additional object of the invention to provide a support system which can be used indefinitely, is economical, and which can be assembled and disassembled by unskilled workers in a few minutes.

Yet another object of the invention is to provide a wall support system which does not require that anchor members be driven into the ground adjacent the wall.

The preceding and other objects are attained by the present invention relating to a method and apparatus for supporting a masonry wall during construction. in a preferred embodiment, a 40 foot long, 20 foot high, 12 inch thick wall section is constructed and supported in the following manner: As the mortar is placed on the top of the foundation wall, a 3 inch X 2 inch X threeeighths inch X2 feet long steel angle member is laid over opposing side edges of the foundation at positions 16 feet apart and 4 feet from each end of the wall. After three courses of face brick for the outer surface and one course of concrete block for the inner surface have been laid, a pair of snap tie members capable of resisting a 5,000 pound tension load are inserted in the motar so that each snap tie extends horizontally from each side of the wall. The snap ties have enlarged ends for a purpose to be described.

After the wall has been constructed to a height of about 10 feet, a horizontal support member such as a 10 feet length of 8 inch channel having a double apertured plate welded to one end is positioned with its inner end in contact with the angle member on the foundation edge so that a pair of studs welded to the angle member will pass through the apertures and be retained by cotter pins. The outer end of each horizontal channel member is permitted to rest on the earth, or preferably, against a pair of planks, 2 inches X 10 inches X 6 feet, for example, or other form of mudsills which serve to distribute downward loading of the channel to the face of the earth. A vertical support member, which may comprise a 10 foot length of 6 inch l-beam is placed against each side of the wall and pinned to a flange extending upwardly from the horizontal channel at a location near the foundation. A pair of elongated slots in the wall engaging flange of the I- beam are placed over the extending ends of the snap tie members and the opposing I-beams on each side of the wall are drawn toward the wall and. each other by hammering wedge-like locking members between the inner flanges and the enlarged ends of the snap tie members. A diagonal member, consisting principally of 3 inch pipe sections is pivotally connected to the horizontal channel member at a location about 3 feet to 4 inches out from the wall, and to the vertical member at a point 5 feet above its lower end. The pipe portions of the diagonal members are spaced from each other to permit the diagonal member to be adjusted in length for the purpose of forcing the vertical l-beam against the wall and the horizontal channel against the ground. This is accomplished by welding a threaded nut member to the free end of one of the pipe sections. The nut member is threadingly engaged with a 2 inch threaded rod member which is telescopically received within the adjacent inner ends of the two spaced pipe sections. The threaded rod member is preferably transversely apertured at several positions along its length to permit the length of the diagonal member to be rapidly adjusted. A pin is placed in whichever aperture which will require the least amount of rotation of the rod to move the pin into engagement with the pipe section which does not carry the nut member. The rod is rotated by placing a bar through one of the unused apertures and using it as a handle to rotate the rod until the diagonal member is extended sufficiently to force the I-beam into tight contact with the wall. It should be understood that the diagonal members on each side of the wall are extended so that the pressure applied against each side of the wall will be relatively uniform. After the diagonal members are tightened, the diagonal members are in compression while the horizontal and vertical members are in tension. The rigid support applied to the upper portion of the wall by the vertical I-beam members causes the wall to behave relative to wind loads in substantially the same manner it behaves after a pair of spaced walls are joined together by a roof or floor structure. Thus, when supported by my improved bracing system, the wall is able to resist approximately four times the moment it could resist if it was a free-standing cantilever.

The principal function of my temporary wall support system is to change the direction of span of the wall from a vertical cantilever to a simple horizontal span. Although a four foot section at each end of the wall is still a cantilever, such a small section is of no concern since the wall is 12 inches thick. The loading of the wall can be described as follows: The wind loads are transferred from the masonry to the vertical brace member on the down-wind side through bending. This member is designed to resist these loads and transmit them to the diagonal member. The diagonal transfers the load to the horizontal channel which rests on a mudsill on the ground. This channel is a tension member, and transfers the loads back to the vertical. Since the vertical members on either side of the wall are fastened together by means of bolting or steel rods located 8 inches to 24 inches above the foundation, the load is transferred through the rods to the brace on the opposite, i.e., windward side of the wall. This brace pushes against the masonry and the load is transferred to the foundation wall through friction between the masonry and concrete. In addition, when the diagonal member is subjected to the above action, it tends to slide the vertical member up on the face of the wall. This is resisted by the angle member fastened to the vertical and embedded into the base of the wall, thus utilizing the entire weight of the wall to resist the force.

If the supported wall is to be extended to a final height of 20-24 feet, the wall is constructed upwardly after it is supported at the -1 2 foot level without embedding any additional elements in it. An upper vertical member is then pinned to the lower vertical member to form an extension thereof and held against the upper section of the wall by an outer diagonal member pinned to the outer end of the horizontal channel member and to the center of the upper vertical member.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a modular wall section supported by two opposed pairs of bracing members in accordance with the invention;

FIG. 2 is a fragmentary end elevational view of a wall with the support system in place;

FIG. 3 is a sectional view taken on the line 33 of FIG. 2;

FIG. 4 is a sectional view taken on the line 4--4 of FIG. 3;

FIG. 5 is a fragmentary, partially sectioned view of the diagonal brace member of the invention and its connection to the horizontal and vertical members;

FIG. 6 is a sectional view of the vertical member coupling taken on line 66 of FIG. 5;

FIG. 7 is a sectional side view, somewhat similar to FIG. 4, showing a modification of the invention, the section being taken on line 77 of FIG. 8; and

FIG. 8 is a sectional view taken on line 88 of FIG. 7 showing a modification of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, my improved bracing system is indicated generally at 10 in supporting relationship with a section of masonry wall 12. The bracing system 10 includes a pair of bracing structures 14, 16 positioned on opposite sides of the wall. Spaced along the wall 12 is a second pair of bracing structures, only one of which, 18, is visible. The spaced pairs of opposed bracing structures cooperate with each other and with the wall 12 to cause wind loads which impinge upon either side of the wall 12 before it is tied into a roof or floor structure (not shown) to be resisted as hereinbefore described. The wall 12 is constructed on top of foundation wall 22 which is preferably of poured concrete construction. Before the first course of bricks 24 and blocks 26 are laid into a bed of mortar 28, a pair of metal angle pieces 30, 30 are laid along the top side edges of the foundation wall 22. A pair of high tensile strength snap tie members 32, 32 are then embedded in the wall as it is being constructed at a location spaced no further than about 2 or 3 feet above the foundation 22 and preferably at a height of about 8 inches or less above the foundation. The snap tie 32 includes notches 32 near each end which permit the ties to be broken off inside the wall 12 after use. The resultant openings left in the wall by the breaking off of ties 32 and the prying out of angles 30 are easily covered with mortar. The ties 32 also have enlarged ends 32" which are contacted by wedge members 34 for tensioning the ties 32 and forcing the vertical members 38 against the wall.

When the wall 12 has been erected to a height slightly higher than the height of vertical I-beam member 38, the erection of the lower portions of braces l4, l6 and 18 can commence with the assembly of the channel-shaped horizontal support members 40 to the angle plates 30. The channels 40 have connecting plates 42 welded to their inner ends. The plates 42 are apertured at 44 (FIG. 3) so that they can pass over studs 46 which are welded to angles 30. The plates 42 are retained against movement away from angles 30 by cotter pins 48. The anchoring of channels 40 to the angles 30 is loose so that the channel may be pivoted up and down 15 or so in each direction to permit the channel to accommodate to the level of the earth adjacent the wall 12. To permit the loading of the channels 40 to be relatively uniformly distributed to the earth 50, a pair of mudsills, 52, 52 such as short lengths of wooden planks, are placed under the channel 40.

After the channels 40 are assembled to the angle member bearing plates 30, the vertical support members 38 are laid against the wall 12 and pinned to brackets 54 welded to channels 40 by pins 56 which may be held in place by cotter pins 58 (FIGS. 3 and 4). Opposed pairs of vertical members 38 are then forced toward each other and the wall 12 by slotted wedge members 34 which provide a wedging action between the ends 32" of the snap tie members 32 and the inner flanges 38' of the I-beam 38. The inner flanges 38' are slotted at 60 to permit the beam to accommodate to a range of vertical positioning of the tie members 32.

As shown in FIG. 5, the vertical member 38 and horizontal member 40 form a triangle having one variable length leg when the diagonal support member 64 is connected to them. The diagonal member 64 includes a lower pipe section 66 pivoted by pin '68 to a bracket 70 welded to the channel member 40. A threaded nut member 72 is welded to the upper end of pipe section 66. An upper pipe section 74 is pivotally mounted by pin 76 to a bracket 78 welded to the vertical support 38 at about its midpoint. Since the diagonal member 64 is always in compression when it is resisting a wind load on the wall 12 it is made adjustable in length by forcing the pipe sections 66, 74 away from each other. This adjustment is made by rotating threaded member 80 relative to threaded nut 72. A series of holes 82 are adapted to receive a pin 84 to permit the length of diagonal 64 to be quickly adjusted to a number of predetermined positions. Final adjustment to compress the member 64 and force the vertical member 38 against the wall 12 can then be made by placing an elongated bar (not shown) in one of the unused holes 82 and rotating the threaded member 80.

After the lower portion of the wall 12 has been supported in the aforementioned manner, the remaining courses of brick and block or other modules can be laid in place. The upper section of the wall is then supported by a vertical support member 138 which may be identical to the lower vertical member 38. Interlocking, generally .l-shaped flanges 86, 186 are welded to one end of each vertical member 38, 138. When the flanges are interlocked as shown in FIGS. 5 and 6, and pins 88 placed through them, the vertical members 38, 138 are locked together in a manner in which either tension or compression forces can be transmitted between them. The upper vertical member 138 is forced against the upper section of the wall 12 by a diagonal member 164 which is identical to diagonal 64 except that pipe section 174 is longer. The lower end of diagonal 164 is pivotally connected to welded bracket positioned at the end of channel 40 and the upper end of the diagonal ispivotally connected to the welded bracket 178 at the center of vertical member 138.

FIGS. 7 and 8 illustrate an alternative embodiment of the invention wherein the means to horizontally tie the vertical support members 238 together and the means to apply the downward loading to the foundation comprise a single set of threaded rod elements 232 rather than the separate snap ties 32 and angled bearing plates 30 shown in the other figures. The rods 232 extend outwardly from each side of the wall through apertures 260 in the vertical members 238 and have nuts 234 on their ends which force the opposed vertical members against the wall 212. The horizontal member 240 is pinned to the vertical member 238 by a pin 256 which 5 passes through an aperture in the bracket 254 which is welded to channel 240. The alternative embodiment of FIGS. 7 and 8 is slightly easier to assemble than the preferred embodiment shown in the other figures but is more difficult to disassemble since the rod 232 must be heavier than the rod 32, preferably about 0.75 in., and is thus thicker than the usual mortar joint. The thickness of the rod prevents its being snapped off and its threads make it difficult to be pulled out of the wall.

I claim:

1. Apparatus for temporarily supporting a freestanding modular wall constructed on top of a foundation against wind damage during construction comprismg:

a first pair of rigid elongated members adapted to be placed vertically against opposing sides of the wall and in contact therewith throughout their lengths;

means extending between said first pair of members intermediate the ends thereof adapted to be placed in said wall as it is being constructed for tying said first pair of elongated members to each other and to said wall and for transferring the stresses insaid members produced by wind loading on the wall to the foundation of the wall; a second pair of rigid elongated members pivotally jointed at corresponding ends thereof to respective ends of said first pair of elongated members and projecting in opposite directions therefrom, said second pair of rigid elongated members being adapted to be supported against downward movement by the ground adjacent said foundation;

a third pair of elongated compression members pivotally connected to each of said first and second pairs of elongated members so as to form a triangular brace on each side of said wall;

one of said pairs of elongated members being adjustable to force said first pair of elongated members towards each other and the wall at the location where said first and third pairs of elongated members are connected to each other.

2. The apparatus of claim 1 wherein said means extending between said first pair of members comprises at least one tie rod member adapted to be placed in the wall at a distance above the foundation and a pair of support plates having portions adapted to lay on top of the foundation and portion extending outwardly from the foundation, each of said pair of support plates being attached to one of said rigid elongated members for supporting the weight of said one member.

3. The apparatus of claim 2 wherein said at least one tie rod member is sufficiently long to extend through at least a portion of each of said first pair of elongated members and includes enlarged portions at its ends which are adapted to cooperate with wedge type fastening means to force said first pair of elongated members against said wall.

4. The apparatus of claim 2 wherein each of said first pair of rigid elongated members includes at least one elongated aperture therein adapted to receive said at least one tie rod member.

5. The apparatus of claim 1 wherein said means extending between said first pair of members comprises at least one tie rod member adapted to be placed on top of the foundation.

6. The apparatus of claim 1 wherein said third pair of elongated members are adjustable in length.

7. The apparatus of claim 6 wherein said third pair of elongated members comprise a pair of hollow end portions and a threaded center portion telescopically receivable inside said end portions, said threaded center portion engaging a threaded portion of one of said hollow end portions and being adjustably movable relative thereto, and means on said center portion for abuting the free end of the other of said hollow end portions.

8. The apparatus of claim 7 wherein said means for abuting comprises a rod, selectively transversely insertable in a plurality of apertures spaced along the length of said threaded center portion, said center portion being adapted to be rotated and thereby moved axially relative to said threaded hollow end portion by inserting an elongated handle in one of said plurality of spaced apertures.

9. The apparatus of claim 1 wherein each of said first pair of elongated members comprises a first section adapted to be placed against said wall and pivotally connected to said second and third pairs of elongated members when the wall is at less than its final height and a second section adapted to be connected to said first section when said wall is at or at least close to its final height, said first and second sections including integral complementary end portions which interlock with each other to permit tension loading of said first pair of elongated members, and a fourth pair of elongated members pivotally connected to said second pair i of elongated members at points remote from said third pair of elongated members and to said second section of said first pair of elongated members at a point spaced upwardly from said end portion.

10. The apparatus of claim 9 wherein said means extending between said first pair of members comprises at least one tie rod member adapted to be placed in the wall at a distance above the foundation and a pair of support plates having portions adapted to lay on top of the foundation and portions extending outwardly from the foundation, each of said pair of support plates being attached to one of said rigid elongated members for supporting the weight of said one member.

11. The apparatus of claim 10 wherein said outwardly extending portions of said support plates engage and retain first end portions of said second pair of elongated members located adjacent the point of connection of said first and second pairs of elongated members, said third and fourth elongated members being connected to said second elongated members at points intermediate the ends thereof and at the ends remote from said first end portions, respectively.

12. The apparatus of claim 1 wherein said means extending between said first pair of members ties said members to each other at locations which are spaced at least about 8 inches above the bottom of said pair of rigid horizontal members.

13. The apparatus of claim 2 wherein said at least one tie rod member ties said first pair of rigid elongated members together at a location between 2 to 36 inches above said support plates. 

1. Apparatus for temporarily supporting a free-standing modular wall constructed on top of a foundation against wind damage during construction comprising: a first pair of rigid elongated members adapted to be placed vertically against opposing sides of the wall and in contact therewith throughout their lengths; means extending between said first pair of members intermediate the ends thereof adapted to be placed in said wall as it is being constructed for tying said first pair of elongated members to each other and to said wall and for transferring the stresses in said members produced by wind loading on the wall to the foundation of the wall; a second pair of rigid elongated members pivotally jointed at corresponding ends thereof to respective ends of said first pair of elongated members and projecting in opposite directions therefrom, said second pair of rigid elongated members being adapted to be supported against downward movement by the ground adjacent said foundation; a third pair of elongated compression members pivotally connected to each of said first and second pairs of elongated members so as to form a triangular brace on each side of said wall; one of said pairs of elongated members being adjustable to force said first pair of elongated members towards each other and the wall at the location where said first and third pairs of elongated members are connected to each other.
 2. The apparatus of claim 1 wherein said means extending between said first pair of members comprises at least one tie rod member adapted to be placed in the wall at a distance above the foundation and a pair of support plates having portions adapted to lay on top of the foundation and portion extending ourwardly from the foundation, each of said pair of support plates being attached to one of said rigid elongated members for supporting the weight of said one member.
 3. The apparatus of claim 2 wherein said at least one tie rod member is sufficiently long to extend through at least a portion of each of said first pair of elongated members and includes enlarged portions at its ends which are adapted to cooperate with wedge type fastening means to force said first pair of elongated members against said wall.
 4. The apparatus of claim 2 wherein each of said first pair of rigid elongated members includes at least one elongated aperture therein adapted to receive said at least one tie rod member.
 5. The apparatus of claim 1 wherein said means extending between said first pair of members comprises at least one tie rod member adapted to be placed on top of the foundation.
 6. The apparatus of claim 1 wherein said third pair of elongated members are adjustable in length.
 7. The apparatus of claim 6 wherein said third pair of elongated members comprise a pair of hollow end portions and a threaded center portion telescopically receivable inside said end portions, said threaded center portion engaging a threaded portion of one of said hollow end portions and being adjustably movable relative thereto, and means on said center portion for abuting the free end of the other of said hollow end portions.
 8. The apparatus of claim 7 wherein said means for abuting comprises a rod, selectively transversely insertable in a plurality of apertures spaced along the length of said threaded center portion, said center portion being adapted to be rotated and thereby moved axially relative to said threaded hollow end portion by inserting an elongated handle in one of said plurality of spaced apertures.
 9. The apparatuS of claim 1 wherein each of said first pair of elongated members comprises a first section adapted to be placed against said wall and pivotally connected to said second and third pairs of elongated members when the wall is at less than its final height and a second section adapted to be connected to said first section when said wall is at or at least close to its final height, said first and second sections including integral complementary end portions which interlock with each other to permit tension loading of said first pair of elongated members, and a fourth pair of elongated members pivotally connected to said second pair of elongated members at points remote from said third pair of elongated members and to said second section of said first pair of elongated members at a point spaced upwardly from said end portion.
 10. The apparatus of claim 9 wherein said means extending between said first pair of members comprises at least one tie rod member adapted to be placed in the wall at a distance above the foundation and a pair of support plates having portions adapted to lay on top of the foundation and portions extending outwardly from the foundation, each of said pair of support plates being attached to one of said rigid elongated members for supporting the weight of said one member.
 11. The apparatus of claim 10 wherein said outwardly extending portions of said support plates engage and retain first end portions of said second pair of elongated members located adjacent the point of connection of said first and second pairs of elongated members, said third and fourth elongated members being connected to said second elongated members at points intermediate the ends thereof and at the ends remote from said first end portions, respectively.
 12. The apparatus of claim 1 wherein said means extending between said first pair of members ties said members to each other at locations which are spaced at least about 8 inches above the bottom of said pair of rigid horizontal members.
 13. The apparatus of claim 2 wherein said at least one tie rod member ties said first pair of rigid elongated members together at a location between 2 to 36 inches above said support plates. 